A major goal of tissue engineering is to provide replacements for malformed, damaged, diseased or worn-out parts of the body. This requires either the accurate reconstitution of body parts, either in vitro or in vivo; or the construction of surrogate body parts of another design which, however, meets the same physiological or structural needs. Efforts at organ reconstitution will be most effective if they are based on an understanding of the principles which determine the organization of cells into properly structured tissues and organs. These principles have been codified in the "differential adhesion hypothesis" (DAH). Through genetic engineering techniques, cDNAs coding for the synthesis and regulated expression of specific adhesion molecules have been introduced into originally non-adhesive cells, generating new cell lines with predetermined adhesive properties. When pairs of such specially designed cell lines were cultured together, they re-assembled to form organ-like structures with the precise structure predicted in advance by the DAH. Additional genetically engineered cell lines designed to test a series of specific predictions of the DAH will be generated. The number of adhesion molecules of each type displaced on their surfaces will be measured, as will the cohesive intensities of aggregates of these cells. From these values the minimal adhesive free energy configurations specific pairs of these cell populations should adopt when combined will be calculated. The actual structures assembled by these cell combinations through cell sorting or tissue spreading will then be observed and compared with these theoretical structures. Our ultimate goals are to solidify the principles specifying the assembly of cells into specific anatomical structures and to demonstrate the ability of genetic engineering techniques to program cells to assemble into such structures. (1) We will engineer cell lines displaying defined amounts of known adhesion molecules. (2) We will measure the densities (sites/cell) of these adhesion molecules. (3) We will measure the cohesive intensities of aggregates of these cells. (4) We will utilize these cell lines to test specific predictions of the DAH concerning their mutual assembly behavior when combined. We anticipate application of both the principals and the techniques employed here to the design of "man- made" organs engineered to carry out specific functions in the human body.